Method of cladding a copper-base metal to an aluminum core



0.002 inch in thickness.

Patented Oct. 7, 1952 UNITED STATE METHOD CLADDINGA' COPPER-BASE I TO AN ALUMINUM CORE Harry B. Burrack, Brooklyn, N}. Y., assignor to Reynolds Metals Company, Richmond, Va.,: a

corporation of Delaware N Drawing. Application April 5,

" Serial No. 659,892

2. Claims. 1

This invention relates to the cladding of aluminum with other metals and has forv its object the provision of an improved method of cladding metal to an aluminum core such as aluminum strip, slabs or ingots. The inven tionis concerned with the bonding of the cladding metal to aluminum in a hot rolling operation in the atmosphere and provides a cladding metal protected from oxidation at temperatures incident to hot rolling, as well as certain steps in the production of the cladding metal and in the rolling of the cladding metal to aluminum.

My invention provides a copper-base cladding metal which includes electrolytic copper and other commercial grades of copper and suitable copper alloys, such as bronze, brass, cupro-nickels and silver nickels, with the bonding surface protected with mechanically adhering aluminum foil, a method of applying the foil, and a method of bonding the foil-protected copper-base metal to aluminum. The aluminum core and the foil may be either pure aluminum orany alloy of aluminum that may be" found'sui-table. In accordance with my invention I heat the cladding metal and the aluminum to temperatures sufiicient to facilitate hot rolling, say from 750 F. to 950 F., and roll at such temperatures in the atmosphere. While I may heat the metals in any suitable manner, my invention permits heating in any ordinary furnace using 1 no special atmosphere, as in the air or in mixtures of combusted gases with air, and transferring the hot metal through the atmosphere to the rolling mill. If the copper-base metals were heated, transferred, or rolled under such oxidizing conditions, a film of oxide would form on the exposed surfaces sufilcient to prevent satisfactory bonding.

I have found that aluminum foil may be rolled onto a suitably conditioned surface of the cladding metal under proper rolling conditions, thereby causing a sort of mechanicaladhesi-on of. the foil which protects the surface from oxidation while it is being heated up to the temperature for hot rolling: .and bonding. I have also found that the foil does not. interfere with the bonding. Any suitable aluminum foil may be used, for example, foil from 0.001 to clean oxide-free surface of the cladding; metal, for example, mechanically as by embossing or abrasive action, or chemically as; by etching, and then to roll the foil and cladding metal together under such pressure as to effect areducti'on in overall thickness of the two metals- Suchreduction in thickness may be in the neighborhood of to for effective results. It is especially advantageous to heat the foil and cladding metal and to roll them together while I prefer to roughen a hot. Therolling at several hundred: degr s above room. temperature gives a better mechanical bond or adhesion of the foil to the cladding metal. The temperature must bekept below the oxidizingrtemperature of the cladding metal which is about 450 F; for copper and 625 F. for brass and the. cupro-nickel alloys. At these temperatures appreciable oxide formation takes place in normal atmospheres.

One of the important features of my invention is the cladding of the aluminum with the other metals by hot rolling in the atmosphere and I accomplish this by protecting the bonding surface of the cladding metal with. an oxygen-excluding barrier in the form of aluminum foil. Av very strong intermetallic bond may be formed between aluminumand. one of the aforementioned cladding metals, by hot rolling. at a temperature which is sufiiciently elevated to cause a sort of interlocking of the two metals at the interface and forming a firmbond' that will Withstand bending and other stresses to.

which the clad metal may be subjected. The most effective hot rolling is carried out at temperatures in the range of 75.9 3. to 950 F. it is desirable, if not essential, to. efiect a substantial reduction in overall thickness during the first pass through the rolls and it is accord;- ingly advisable to roll at temperatures near the upper limit. The reduction; in thickness, in addition to the temperature, is significant in that it; efiectuates such a working of the, metals on the, initial pass as to form an intermetallic bond. The greater metallic activity at high temperature plus the greater metal flow due to excessive working. cause the metals to infuse with each other at the interface. After the first pass, the metal may be sent through the rolls with a plurality of passes sufficient to reduce thermetal to any desired gauge thickness:

The invention is applicable to the, bonding of the cladding metal to aluminum strip... slabs or ingots. In. bonding to strip it is advantageous to use coils of both the cladding metal and the aluminum core which are of the same width and preferably the same length. The cladding? metal is previously-rolled with aluminum foil, j

as above described, and thencoiled. Both coils are heated in any suitable wayto a hot rolling temperature of from 750 F; to 950 F The for use or finishing, or, rolled to gage whilenhot: I If coiled and cooled, the metal maybe rolled,

to gage at any time. The first pass effects such an interfacial dispersion of the metals that-the aluminum foil loses its identity and becomes terial.

part of a' strongfirm'bond between the metals.

In a somewhat similar operation, I may*apply the'foil protectedcladding metal to a slab or an ingot of aluminum. For example, I may 3 apply a cooper sheet 0.1 inch thick to a 2inch thick slab of aluminum. I may, accordingly,

num

When I refer to hot rolling, I refer to any suitable hot rolling, and especially to the conventional hot rolling in standard mills. The rolling is, of course, carried out in the atmosphere.

The invention is described in connection with bonding a cladding metal-to one surface of the aluminum core. :Myinvention applies to, the similar bonding of cladding metal to both surfaces of the'aluminum core. Both'surfaces of the core maybe clad by repeating the operation above described, using two sheets of copper and by rolling both cladding metal sheets, one on each surface, to. thecore inthe same operation;

The following examples illustrate methods. of

the invention:

. Example I Surface cleaned and mechanically roughened copper strip of 0.008 inch gage, 26 inches wide and 200 feet long was given a preliminary heat preferably of from 300 F. to 125 F., which is below the oxidizing temperature. This "strip was coiled for "convenient;handling. The coil was transferred to ajrollingmill, and as it was fed to the rollsit was surfaced'by ammmu'm foil led down from an upper roll; the aluminum-foil being,of 0.001 inch in thickness. The overall rolling reduction of thecomposite coppe'r; and foil'was about' At "the end of the rolling mill thecomposite stripwas coiled. It was then heated to about-850F: and repassed through the rolling mill along with analuminum strip of about 0.081 inch thickness-'at'the same temperature, the foil face being interposed. As the-compositecopper and foil strip is fed through the roll-,yit'is' bonded to 'the aluminum strip. 1 For satisfactory bonding-the first pass should effect a heavy reduction, say, in overallthickness. The rolling operation mayreduce-fthe copperfoil composite strip to 0.006 inch and the aluminum strip to 0.058 inch on the finished ma- 7 If it is desired to clad both faces of'th'e aluminum strip with copper, .the procedure is altered accordingly, composite copper-foil strips being prepared and heated preliminary'to rolling with the aluminum strip and interposed oriboth faces of the latterstrip. 1

Ewample I! aluminum slab 2,-inches thick, 26 inches wide and 100 inches long, and a copper; sheet 0.109 inch" thick, 26 inches wide and 100 inches long are to be bonded. Aluminum foil 0.001 inch in thickness and of the same; dimensions as, the copper sheet wasplaced over the copper. sheet and both metals were'heated to about-4259B; and transferred to the rolling mill and the foil facing rolled thereon. In the rolling of the foil.

vonlthe cop'persheet I-prefer a "reduction of 10 of the composite body,v but the reduction may begreaten f Notwithstanding a reduction by the rolls of the copper-foil composite body to the extent of 10%, only a mechanical bond of the two metals was eifected. To achieve an intermetallic bond the temperature must be raised above that temperature which results in appreciable oxide formation on unprotected copper.

The foil protected copper sheet is then heated to about "850 F., and the aluminum slab is given a corresponding'heat. The two pieces, aluminum slaband copper sheet, were then brought and hot rolled. On the first pass through the mill the overall thickness of both metals was reduced about 20%. A plurality of passes was then used'to reduce thejmaterial to any desired finishgage.

Iclaim: 1. In the cladding of a copper-base metal to an aluminum core the method which comprises heating the, copper-base metal to a temperature of from300 F. to 425 F. and rolling aluminum foil thereon while hot to form a mechanical bond 'therehetween, heating the copper-base metalwith the foil attached and the aluminum core to-a hot rolling temperature of at least 750 F., and subjecting the; heated metals while at a temperature which facilitates roll reduction thereof to a rolling operation to efiect a substantial overall reduction, thereby firmly bonding the copper-base metalto the aluminum.

' 2. In the cladding of ajcopper-base metal to an aluminum core-the method which comprises heatingv a co ziper-base metal strip having its the aluminum core.

v HARRY B. BURRACK.

REFERENCES CITED The-following references are of record in the file of this" patent: V

UNITED STATES PATENTS Number Name Date 685,479 Wachwitz Oct. 15, 1901 929,778; Monnat Aug. 3, 1909 958,651 .I-Ieeren May 17, 1910 1,660,246 Willem; Feb. 21,1928

1,667,787, Jaeger May 1, 1928 1,679,308 Jordan"; July 31, 1928 1,934,673 Klemperer Nov. '7, 1933 2,171,040 Merritt Aug. 29, 1939 2,383,511 1 Reynolds Aug. 28, 1945 FOREIGN PATENTS Number I I ,7 Country Date l1,82l Norway May 4, 1903 520,365 Great Britain Apr. 22, 1940 OT-HER REFERENCES Aucojmprehensive Treatise on Inorganic and Theoretical Chemistry, vol. III, p. 131, Longmans, Green and Co; London, England, 1927. 

1. IN THE CLADDING OF A COPPER-BASE METAL TO AN ALUMINUM CORE THE METHOD WHICH COMPRISES HEATING THE COPPER-BASE METAL TO A TEMPERATURE OF FROM 300* F. TO 425* F. AND ROLLING ALUMINUM FOIL THEREON WHILE HOT TO FORM A MECHANICAL BOND THEREBETWEEN, HEATING THE COPPER-BASE METAL WITH THE FOIL ATTACHED AND THE ALUMINUM CORE TO A HOT ROLLING TEMPERATURE OF AT LEAST 750* F., AND SUBJECTING THE HEATED METALS WHILE AT A TEMPERATURE WHICH FACILITATES ROLL REDUCTION THEREOF TO A ROLLING OPERATION TO EFFECT A SUBSTANTHEREOF TO A ROLLING OPERATION TO EFFECT A SUBSTANTIAL OVERALL REDUCTION, THEREBY FIRMLY BONDING THE COOPER-BASE METAL TO THE ALUMINUM. 